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Tuberculosis hit a prestigious San Francisco high school, spreading from a single case to hundreds of infections in just months. What started as a missed diagnosis in a boarding student escalated into a full-blown outbreak — 244 latent and 8 active TB cases among students and staff. It's a stark reminder that TB is very much a modern threat.
When a physician heard through casual conversation that a San Francisco high school was dealing with tuberculosis, it seemed almost unbelievable. But by March 2026, what began as a single missed diagnosis at Archbishop Riordan High School (ARHS) had grown into one of the most striking TB outbreaks in recent U.S. history.
The index case — a recently immigrated student living in the school's boarding facility — presented with a cough in September 2025, but TB wasn't initially suspected. By the time the student was referred to the San Francisco Department of Public Health in November, months of close indoor contact had already seeded the outbreak. Mandatory school-wide testing followed, and the numbers were alarming.
By the Numbers:
Why it matters: TB cases in the U.S. have been quietly rising since 2021, driven by public health funding cuts, pandemic-related disruptions, and increased immigration from high-prevalence regions. The ARHS outbreak illustrates how quickly a single missed case — in the wrong setting — can spiral. It's a timely reminder that complacency about tuberculosis carries real consequences.
